Incidence and Toxigenicity of SeedborneFusariumSpecies from AnnualMedicagoSpecies in South Africa

Abstract

Six Fusarium species were isolated from seed of annual Medicago species (M. littoralis and M. truncatula) in a field grazed by sheep near Swellendam, South Africa. F. acuminatum was the predominant fungus isolated from seeds collected during summer and F. reticulatum from seeds collected during winter, F. avenaceum, F. equiseti, F. graminearum Gr. 1 and F. sambucinum occurred less frequently. Cultures on autoclaved corn of five single-conidial isolates of each of the six Fusarium species were tested for toxicity in day-old ducklings. All Fusarium isolates with the exception of four isolates of F. equiseti caused 100% mortality. Cultures on corn of one isolate of each species were dosed to sheep by means of a stomach tube: F. acuminatum, F. avenaceum, and F. reticulatum were lethal. Single doses of 5 g/kg of culture material of F. acuminatum and F. reticulatum caused death within 2 and 18 hr, respectively, whereas culture material of F. avenaceum administered twice at 5 g/kg caused death within 48 hr. Moniliformin was the most abundant of five mycotoxins analyzed in culture material of the three species lethal to sheep. A single dose of 10 mg/kg of crystalline moniliformin resulted in death of a sheep within 18 hr. These results indicate that toxigenic Fusarium species associated with medic seeds present a potential hazard to grazing animals.